Kommentar zu Wajikra 25:41

הוא ובניו עמו [AND HE SHALL GO AWAY FROM THEE] BOTH HE AND HIS CHILDREN WITH HIM — Rabbi Simeon asked: If he sold himself who sold his children that Scripture has to state they shall leave the master together with him? But we may learn from this that the master is bound to provide his (the servant’s) children with food (Kiddushin 22a; cf. Rashi on Exodus 21:3) although they are not his slaves.

This master is obligated to feed his children. (Kitzur Mizrachi) It is not talking about any sons, but [only] of sons whom the father is obligated to feed; i.e., until they are six years old.

הוא ובניו עמו, “he and his sons with him.” Generally speaking, people who sell themselves are destitute. This being so, it may be assumed that when the father sold himself he included his children in the sale and they had agreed to this as where would they find sustenance if not with the father’s master?